Verfahren zur Dehydratisierung von Pyromellithsaeure

摘要

Pyromellitic acid is dehydrated by (a) adding to the pyromellitic acid an inert org. cpd. which is liquid at the reaction temp. and forms an azeotropic mixt. with water, (b) heating under pressure at 100-300 degrees C pref. 200-250 degrees C and distilling the mixt. or org. cpd./water until the release of steam ceases, and (c) recovering the pyromellitic dianhydride from the residual liquid phase. Title cpd. is used for the prepn. of plasticisers and resins. The filtrate obtd. after removal of the dianhydride can be used directly for oxidn. reactions without prior purification.